This application claims the priority benefit of Taiwan application serial no. 90114489, filed Jun. 14, 2001.
1. Field of the Invention
This invention relates in general to a charging device, and more specifically relates to a charging device suitable for a rechargeable battery of a portable device.
2. Description of Related Art
Digital electronic products have brought more convenient life for human beings as they have been highly developed. Furthermore, high developments of a variety of portable digital devices, such as a mobile phone, a notebook computer (notebook) or a personal digital assistance (PDA), considerably increase convenient life and work efficiency for human beings. As for the notebook, due to its portability, the power supplied to the notebook depends on a special battery installed therein. Therefore, it is very important that the power of the battery is continuously and stably supplied to the notebook for maintaining normal operations of the notebook. Accordingly, charging ability and charging time are important criteria for evaluating a notebook.
FIG. 1 shows a block diagram for a system block 100 of a conventional notebook. As shown, The conventional system block 100 is coupled to an external power source 102, and the system block 100 comprises a charging device 103 and a main function device 104. The charging device 103 utilizes the external power source 102 to charge a rechargeable battery 106. The charging device 103 comprises a current detecting device 108 for detecting a charging current fed into the rechargeable battery and then outputting a charging current signal according to the detected charging current. FIG. 2 shows a block diagram of the current detecting device 108. The current detecting device 108 consists of a current detecting resistor 202 and a current to voltage convert circuit 204, which connection is as shown in FIG. 2. When the charging device 103 begins to charge rechargeable battery 106, the charging current flows through the current detecting resistor 202 and a voltage drop occurs over the current detecting resistor 202. As the charging current becomes larger, the voltage drop increases, too. Therefore, by means of the current detecting resistor 202, the current to voltage convert circuit 204 is able to detect the charging current and then outputs a proper voltage according to the detected charging current. The outputted voltage is defined as the charging current signal, representing the magnitude of the charging current.
Referring to FIG. 1 again, the charging current signal from the current detecting device 108 is fed to a current error amplifier 110. The current error amplifier 110 is coupled to the current detecting device 108 for receiving the charging current signal from the current detecting device 108 and a predetermined charging current signal Cs of the charging device. The current error amplifier 110 compares the detected and predetermined charging current signals for setting and adjusting the charging state of the charging device 103. A DC-DC converter power stage 112 is coupled to the current error amplifier 110 for adjusting the charging current inputted to the current detecting device 108 according to a charging current adjustment signal, thereby the charging state of the charging device 103 can be adjusted. Additionally, the voltage of the rechargeable battery 106 is also feedback to a voltage error amplifier 114. The voltage error amplifier 114 receives a charging voltage signal of the rechargeable battery 106 and a predetermined charging voltage signal Vs of the charging device 103, and then accordingly generates a charging voltage adjustment signal to the DC-DC converter power stage 112. The DC-DC converter power stage 112 receives the charging current adjustment signal from the current error amplifier 110 and the voltage adjustment signal from the voltage error amplifier 114 to adjust the charging power. In other words, the charging device 103 can adjust and determine the charging condition during charging the rechargeable battery 106 according to the charging current inputted to the rechargeable battery 106 and the charging voltage of the rechargeable battery 106 itself.
FIGS. 3Axcx9c3C show timing diagrams that the charging voltage and the charging current are varied with time when the charging device 103 charges the rechargeable battery with a full rated current. Assuming an initial charging voltage Vi of the rechargeable battery 106, the initial charging voltage Vi is smaller than a full rated voltage Vf of the rechargeable battery 106. The charging device 103 determines the full rated voltage Vf of the rechargeable battery 106 according to the predetermined charging voltage signal previously inputted to the voltage error amplifier 114. When the charging process begins, both of the charging current adjustment signal from the current error amplifier 110 and the charging voltage adjustment signal from the voltage error amplifier 114 are inputted to the DC-DC converter power stage 112, in which both adjustment signals are represented by their voltages. Because the voltage Vi of the recharging battery 106 is smaller than its full rated voltage Vf, the charging voltage adjustment signal outputted from the voltage error amplifier 114 is smaller than the charging current adjustment signal outputted from the current error amplifier 110. Accordingly, the DC-DC converter power stage 112 adjusts the charging state based upon the received charging current adjustment signal, and then the charging device 103 charges the rechargeable battery 106 with a full rated current Is. The full rated current Is is determined by the charging device 103 according to a predetermined charging current signal previously inputted to the current error amplifier 110. For example, as shown in FIG. 3A, the full rated current Is3 is inputted to the rechargeable battery 106.
Referring to FIG. 3A, as the charging time increases, the voltage of the rechargeable battery 106 increases. The voltage level of the charging voltage adjustment signal increases as the voltage of the rechargeable battery 106 increases, but is still smaller than the voltage level of the charging current adjustment signal outputted from the current error amplifier 110. Therefore, the DC-DC converter power stage 112 adjusts the charging state according to the received charging current adjustment signal such that the charging current is maintained at the fall rated current Is3 preset by the charging device 103.
For example, as shown in FIG. 3A, when the charging process proceeds to time t3, the charging voltage of the rechargeable battery 106 is equal to the predetermined full rated voltage Vf of the rechargeable battery 106. Thereafter, the voltage level of the charging voltage adjustment signal outputted from the voltage error amplifier 114 is larger than the voltage level of the charging current adjustment signal outputted from the current error amplifier 110. The DC-DC converter power stage 112 adjusts the charging state according to the received charging voltage adjustment signal. Then, the charging current for the rechargeable battery 106 decreases as the time increases. Furthermore, the voltage of the rechargeable battery is maintained at the full rated voltage Vf.
As the foregoing description, the full rated current Is inputted to the rechargeable battery 106 is previously determined by the charging device 103. And the value of the full rated current Is determines the charging efficiency, i.e., how much time the charging process spends. FIG. 3B shows a diagram that the charging voltage of the rechargeable battery 106 increases with time during the charging process when the full rated current inputted to the rechargeable battery 106 is Is2. Referring to FIGS. 3B and 3C, because the full rated current Is2 is larger than the full rated current Is1, the charging time t2 using the full rated current Is2 is less than the charging time t1 using the full rated current Is1. Similarly, referring to FIGS. 3A, 3B and 3C, when the rechargeable battery 106 is charged by a full rated current Is3 larger than the full rated current Is1 or Is2, the charging time t3 is less than the charging time t1 using the full rated current Is1 or the charging time t2 using the full rated current Is2. In other words, when the predetermined full rated current Is is larger, its charging efficiency is better. Namely, the charging process spends less time.
As the foregoing description, the charging device 103 determines the full rated current Is and the full rated voltage Vf for charging the battery by previously setting the charging current signal and the charging voltage signal. Therefore, during the charging process, both the full rated current Is and the full rated voltage Vf are preset and as constant, which means that the maximum power reserved for charger is a constant when the charging device 103 charges the battery 106. But not totally utilized.
The external power source 102 also supplies a portion of its output power to the main function device 104 of the notebook when the charging device 103 charges the rechargeable battery 106. Referring to FIG. 1, a power source mix circuit 116 is coupled to the external power source 102 and the rechargeable battery 106 for providing power to the main function device 104 of the notebook to maintain its normal function.
The charging device is coupled to the external power source. The external power source also provides power (the work power) for the operation of main function device of the notebook in addition to providing power (the charging power) to the charging device. The power provided by the external power source is constant and must be properly distributed for maintaining the normal function of the main function device and effectively charging the rechargeable battery. The charging device determines the full rated current and the full rated voltage for charging by previously setting the charging current and the charging voltage. In other words, the charging power distributed and reserved for the charging device to charge the battery is constant. However, the power consumed by the main function device during its operation is changed with its tasks, rather than a constant. Accordingly, it has to properly set the full rated current and full rated voltage of the charging device for preventing the total of the charging power and the work power from exceeding the output power of the external power, i.e., to prevent overloading. Conventionally, the charging power of the charging device is set according to the maximum work power of the main function device of the notebook during its operation. Namely, the maximum charging power is set by subtracting the maximum work power of the main function device from the output power of the external power source. Accordingly, even though the notebook is operated with its maximum work power, the external power source is not overloaded.
However, there are some problems happened to the conventional charging device. The maximum charging power of the charging device is set according to the maximum work power of the main function device of the notebook during its operation. FIG. 4 is a timing diagram for illustrating the uneffective power, the work power of the main function device and the charging power of the charging device distributed from the output power of the external power source, wherein the horizontal axis represents time and the vertical axis represents percentages of charging power of the charging device and the work power of the main function device with respect to the output power of the external power source, assuming that the output power of the external power source is 100%. It should be noticed that the output power of the external power source is not completely provided to the main function device or the charging device, and a small portion of the output power is unused. Furthermore, the notebook is not always operated with its maximum work power and the charging device is not always charging a rechargeable battery with maximum charging power. Therefore, the sum of the work power of the main function device and the charging power of the charging device is smaller than the total output power of the external power source. A portion of the output power, the shadow portion in FIG. 4, of the external power source is not efficiently used. The shadow portion is wasted and termed as the uneffective power. In other words, the usable output power of the external power source is not completely utilized. Therefore, it requires a longer time to charge the rechargeable battery and the charging efficiency is not good.
According to the discussion setout, the conventional charging device encounters problems that the output power is not completely utilized, charging time is long and the charging efficiency is bad.
According to the foregoing description, an object of this invention is to provide a charging device capable of dynamically adjusting a charging power, for increasing the utility of the output power of the external power source, reducing the charging time and increasing the charging efficiency.
According to the object mentioned above, the invention provides a charging device capable of dynamically adjusting a charging power.
The charging device is within a system block of a portable system. The system block consists of the charging device and a main function device, and an external power source is coupled to the system block for supplying a work current to the main function device and for charging a rechargeable battery in the charging device. The charging device comprises elements as follows. A DC-DC converter power stage is coupled to the external power source for supplying a charging current to the rechargeable battery. A current error amplifier is coupled to the DC-DC converter power stage for setting a charging current adjustment signal according,.to a charging current signal and a work current operation signal, and the charging current adjustment signal is fed to the DC-DC converter power stage for adjusting the charging current. A first current detecting device is coupled to the DC-DC converter power stage, current error amplifier and the rechargeable battery for outputting the charging current signal to the current error amplifier based upon the charging current. Additionally, the charging current is fed to the rechargeable battery to charge the rechargeable battery. And, a current detecting/comparating device is coupled to the external power source and the current error amplifier for outputting the work current signal to the current error amplifier by means of comparing and operating the work current and a work current setting signal.